Children and adolescents with Down syndrome (DS) are reported, variously, to have language skills above (vocabulary comprehension) and below (expressive syntax) their nonverbal mental age; cross-sectional evidence suggests that the deficits increase with age. The goals of the present work are to determine, through longitudinal study, whether the gaps between the cognitive level of children with DS and their expressive and receptive language levels widen with age and to identify acquisition processes associated with variation in language skill with DS children. This competing continuation proposal extends the period of longitudinal study of 5 DS children and adolescents aged 5 to 21 years from two to six years and the number of DS observation points from two to four. It permits a definitive longitudinal test of the cumulative deficit hypothesis and, in doing so, permits an empirical test for an elaborated theory of language production development (Child Talk) that would not be possible in normally developing children, whose cognitive and language skills do not ordinarily diverge widely. Computer analyses of the free speech transcripts will permit a detailed longitudinal description of changes in the syntax, semantics, and pragmatics of spoken language in children with DS over the six year period. Hierarchical linear modeling will be used to evaluate between-s predictors of rates of growth in the language variables. In addition, new studies of DS children's ability to narrate and recall novel events, to "fast map" novel word meaning from event and story contexts, and to benefit from prior discourse use of words and sentence structure in utterance formulation will be conducted, elaborating the experimental investigations of narration, vocabulary acquisition, and prior discourse priming on the basis of outcomes in the current grant period. Experimental tasks evaluating comprehension strategies will be added. Performance on all tasks will be compared to three groups of normally developing children statistically matched for 1) nonverbal mental age and SES; 2) language comprehension and SES; and.3) language production and SES. Within the DS group, experimental task performance will be analyzed for variation as a function of cognitive, comprehension, and production skills in a test of the Child Talk model.